1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor using oxotitanyl phthalocyanine (TiOPc) as a charge generating material, and also relates to a coating liquid for a charge generating layer for producing the same and a method for manufacturing the same.
2. Description of the Related Art
In image forming apparatuses such as a printer, a laser light source, in particular a small-sized semiconductor laser light source of high reliability, is used instead of a white light source, to realize image formation of high speed, high image quality and non impact.
Electrophotographic photoreceptors installed in image forming apparatuses are classified into inorganic photoreceptors and organic photoreceptors. Typical inorganic materials used as the inorganic photoreceptor include selenium (Se) containing materials such as amorphous selenium (a-Se) and, amorphous arsenic selenium (a-AsSe), zinc oxide (ZnO), cadmium sulfide (CdS) and amorphous silicon (a-Si), which have been subjected to dye sensitization and dispersed in a binder resin, but they are substantially not applied to practical use due to various problems. Specifically, a photoreceptor using Se containing material or CdS is inferior in heat resistance and storage stability, and involves a problem in disposal. A photoreceptor using ZnO is low sensitive and poorly durable. A photoreceptor using a-Si is low in causing environmental pollution and is highly sensitive and highly durable, but it brings about image defects caused by a production process, i.e., a plasma CVD (chemical vapor deposition) method, and has low productivity, which causes an increase in production cost.
On the other hand, since the organic materials used for the organic photoreceptor include many kinds of materials, a photoreceptor having high storage stability and low toxicity can be obtained by selecting an appropriate one from among the materials, and formation of a thin film can be easily conducted by coating at a low production cost. Thus, improvements in sensitivity and durability have been rapidly realized in recent years. Such materials include bisazo type compounds, squaric acid methine type dyes, indoline type dyes, cyanine type dyes, pyrylium type dyes and phthalocyanine type compounds.
It is firstly desirable in a photoreceptor installed in an image forming apparatus using a laser light source to exhibit high sensitivity to light of a long wavelength band of about 800 nm, which is the wavelength band of the laser light source. A photoreceptor using a bisazo type compound has low sensitivity to light of a long wavelength band. A photoreceptor using a squaric acid methine type dye, indoline type dye, cyanine type dye or pyrylium type dye has relatively high sensitivity to light of a long wavelength band, but is inferior in stability of reiteration characteristics. Therefore, these organic materials cannot be subjected to practical use. A photoreceptor using a phthalocyanine type compound has high sensitivity to light of a long wavelength band and higher stability than the other materials. In particular, a photoreceptor using TiOPc has high sensitivity.
The phthalocyanine type compounds have different sensitivity peaks and physical properties depending on whether a central metallic atom is present or not and on the species thereof, and the physical properties vary depending on the crystal forms thereof. Accordingly, it is necessary to include the crystal form in criteria for judging whether the compounds can be used for a photoreceptor. The crystal forms of TiOPc are classified by difference in diffraction angle of an X-ray diffraction spectrum in Denshi Shashin Gakkai-shi (The Society Journal, Society of Electrophotography of Japan), (Vol.32, No. 3, 1993): 282-289) Japanese Unexamined Patent Publication JP-A 61-239248 (1986) discloses a type, Japanese Unexamined Patent Publication JP-A 62-67094 (1987) discloses A type, Japanese Unexamined Patent Publication JP-A 64-17066 (1989) discloses Y type, Japanese Unexamined Patent Publication JP-A 3-54264 (1991) discloses M-xcex1 type, and furthermore C type, M type and I type are present. The crystal types of TiOFc, the lattice constants of which have been known, are C type, Phase I type and Phase II type. Phase II type is of the triclinic system, and Phase I type and C type are of the monoclinic system. Prom the crystal lattice constants, A type and I type belong to Phase I type, xcex1 type and xcex2 type belong to II type, and M type belongs to C type. Furthermore, Japanese Unexamined Patent Publication JP-A 10-237347 (1998) discloses a photoreceptor using crystalline TiOPc exhibiting a specific X-ray diffraction spectrum.
Secondly, the photoreceptor is desired to form an image without generation of interference fringes. Because laser light has a single wavelength, incident light on a photosensitive layer and reflected light on a support interfere at an interface of the photosensitive layer with the support to form an interference fringe. As precautionary measures against generation of interference fringes, the following measures are disclosed in Denshi Shashin Gakkai-shi (The Society Journal, Society of Electrophotography of Japan), (Vol.32, No. 3, 1993): 282-289), i.e., (1) a surface of the support is roughened by cutting, spiral cutting, blast processing or anodic oxidation, (2) the surface of the support is appropriately roughened by coating an electroconductive layer using slectroconductive particles, (3) particles scattering light are incorporated into an adhesive layer between the support and the photosensitive layer, and (4) a photoreceptor is made transparent. The measures (1) to (3) are related to irregularly reflecting light, and the measure (4) is related to transmitting incident light. As a specific example of the measure (4), Japanese Unexamined Patent Publication JP-A 8-194322 (1996) discloses a technique in that an organic photoelectroconductive transparent sheet formed by accumulating an organic photoelectroconductive layer on a transparent electroconductive base sheet is wound on a support having a surface made black.
In the measure (1), however, the support must be separately processed. In the measure (2), another layer must be provided. In the measure (3), particles must be newly introduced. There is a possibility that these bring about deterioration in coating properties of a coating liquid and deterioration in electric characteristics. In the measure (4), the material for the electroconductive support itself must be changed, resulting in an increase in production costs.
An object of the invention is to provide an electrophotographic photoreceptor which exhibits high sensitivity to laser light and can form an image without forming an interference fringe, to provide a coating liquid for a charge generating layer for forming the photoreceptor, and to provide a method for manufacturing an electrophotographic photoreceptor, by which the photoreceptor can be produced with excellent coating properties and high electric characteristics at a low cost.
The invention relates to an electrophotographic photoreceptor comprising:
an electroconductive support; and
a photosensitive layer on the electroconductive support, including at least a charge generating layer and a charge transporting layer accumulated thereon,
the charge generating layer containing oxotitanyl phthalocyanine as a charge generating material,
the charge generating layer having a Y value of 37 or less, which Y value is one element of three excitation values in XYZ color system showing an object color.
According to the invention, the photoreceptor exhibits high sensitivity to laser light since TiOPc is contained, and an image can be formed without generation of an interference fringe due to laser light since the Y value is 37 or less. In the invention, the Y value is used as an index showing the darkness or lightness of the charge generating layer. The Y value is one element of the three excitation values in the XYZ color system showing an object color, and can be measured by a commercially available colormeasuring apparatus, for example, MCPD-2000 produced by Otsuka Electronics Co., Ltd. The larger the Y value is, the smaller the film thickness is, and since a Y value of more than 37 produces an interference fringe on an image, the Y value needs to be 37 or less. The interference fringe is a phenomenon which is caused in such a case where incident light is not completely absorbed in the charge generating layer and is released as reflected light, which interferes subsequent incident light. When the Y value is more than 37, the color of the charge generating layer is too light, and absorption of the incident light becomes insufficient, whereby reflected light is formed to generate the interference fringe.
The photoreceptor of the invention is realized by containing TiOPc as a charge generating material and by making the charge generating layer to have the Y value to 37 or less, and there is no necessity to separately process the surface of the support, to form another layer on the support, or to mix a light scattering substance in the adhesive layer between the support and the charge generating layer for irregular reflection of incident light. Therefore, the coating property upon forming the layer on the support is not deteriorated, and the electric characteristics of the photoreceptor are not deteriorated. It is also not necessary to change the material for the electroconductive support itself to make it transparent. Thus, the invention does not bring about increase of the production cost.
In the invention it is preferable that the Y value of the charge generating layer is 35 or less.
According to the invention, the Y value is 35 or less, and accordingly the interference fringe caused by the incident light and the reflected light on the support of the laser light is stably suppressed in image formation.
In the invention it is preferable that the oxotitanyl phthalocyanine has major diffraction peaks at Bragg angles (2xcex8xc2x10.2xc2x0) of 7.3xc2x0, 9.4xc2x0, 9.6xc2x0, 11.6xc2x0, 13.3xc2x0, 17.9xc2x0, 24.1xc2x0 and 27.2xc2x0 in an X-ray diffraction spectrum.
According to the invention, the charge generating layer contains the TiOPc having the diffraction peaks, so that the photoreceptor exhibits high sensitivity to the laser light.
In the invention it is preferable that in the X-ray diffraction spectrum of the oxotitanyl phthalocyanine, a bundle of peaks formed by the diffraction peaks at the Bragg angles (2xcex8xc2x10.2xc2x0) of 9.4xc2x0 and 9.6xc2x0 which overlap each other, is a maximum intensity of diffraction, and the peak at the Bragg angle (2xcex8xc2x10.2xc2x0) of 27.2xc2x0 is a second maximum intensity of diffraction.
According to the invention, the charge generating layer contains the TiOPc having the diffraction peaks in the X-ray diffraction spectrum, so that the photoreceptor exhibits further high sensitivity to the laser light.
The invention also relates to a coating liquid for a charge generating layer of an electrophotographic photoreceptor comprising an electroconductive support, and a photosensitive layer on the electroconductive support, including at least a charge generating layer and a charge transporting layer accumulated thereon, the coating liquid comprising oxotitanyl phthalocyanine as a charge generating material, and having a turbidity in a range of from 180 to 350.
According to the invention, the coating liquid containing TiOPc and having a turbidity adjusted to a range of from 180 to 350 is coated on an electroconductive support, so as to produce the charge generating layer. The turbidity herein is an index expressing an extent of turbidity caused by insoluble matters in a liquid, and is defined as a ratio (Td/Tp), when parallel light is incident from a light source on a cell filled with the liquid, of light scattered by turbidity in the liquid (Td: diffusion transmitted light) to light transmitted as parallel (Tp: parallel transmitted light). The turbidity can be measured by a commercially available turbidity meter, such as SEP-PT-501D produced by Mitsubishi Kasei Co., Ltd. The photoreceptor having such a charge generating layer exhibits high sensitivity to the laser light owing to TiOPc contained, and can form an image without generating an interference fringe due to the laser light. In the invention, the interference fringe can be suppressed by making the turbidity of the coating liquid 180 or more. However, when the turbidity exceeds 350, the electric characteristics are deteriorated due to defective dispersion. Therefore, it is necessary that the turbidity is 350 or less. The interference fringe is a phenomenon caused by the mechanism in that incident light is not completely absorbed in the charge generating layer to be released as reflected light, which interferes subsequent incident light. When the turbidity is less than 180, the color of the charge generating layer thus formed is too light, and absorption of the incident light becomes insufficient, whereby reflected light is formed to generate the interference fringe.
In general, when the Y value becomes small, the film thickness of the charge generating layer becomes large, whereby the electric characteristics are enhanced, particularly the residual potential is increased. However, by using the coating liquid having the turbidity according to the invention, a low Y value can be realized even in the case where the film thickness of the charge generating layer is small, and thus the generation of interference fringe and the increase of residual potential can be suppressed at a time.
Furthermore, because the charge generating layer of the photoreceptor is produced by using the coating liquid containing TiOPc as a charge generating material and having a turbidity in a range of from 180 to 350, there is no necessity to separately process the surface of the support, to form another layer on the support, or to mix a light scattering substance in the adhesive layer between the support and the charge generating layer for irregular reflection of incident light. Therefore, the coating property upon forming the layer on the support is not deteriorated, and the electric characteristics of the photoreceptor are not deteriorated. It is also not necessary to change the material for the electroconductive support itself to make it transparent. Thus, the invention does not bring about increase of the production cost.
In the invention it is preferable that the turbidity of the coating liquid is in a range of from 200 to 350.
According to the invention, when the turbidity of the coating liquid is 200 or more, a charge generating layer produced by the coating liquid can stably suppress the interference fringe to form an image.
In the invention it is preferable that the oxotitanyl phthalocyanine in the coating liquid to produce the charge generating layer has major diffraction peaks at Bragg angles (2xcex8xc2x10.2xc2x0) of 7.3xc2x0, 9.4xc2x0, 9.6xc2x0, 11.6xc2x0, 13.3xc2x0, 17.9xc2x0, 24.1xc2x0 and 27.2xc2x0 in an X-ray diffraction spectrum.
According to the invention, the coating liquid comprises the TiOPc having the diffraction peaks in the X-ray diffraction spectrum, so that an electrophotographic photoreceptor can be produced that exhibits high sensitivity to the laser light.
In the invention it is preferable that in the X-ray diffraction spectrum of the oxotitanyl phthalocyanine in the coating liquid to produce the charge generating layer, a bundle of peaks formed by the diffraction peaks at the Bragg angles (2xcex8xc2x10.2xc2x0) of 9.4xc2x0 and 9.6xc2x0 which overlap each other, is a maximum intensity of diffraction, and the peak at the Bragg angle (2xcex8xc2x10.2xc2x0) of 27.2xc2x0 is a second maximum intensity of diffraction.
According to the invention, the coating liquid comprises the TiOPc having the diffraction peaks in the X-ray diffraction spectrum, so that the photoreceptor which exhibits further high sensitivity to the laser light can be produced.
The invention also relates a method for manufacturing an electrophotographic photoreceptor comprising an electroconductive support, and a photosensitive layer on the electroconductive support, including at least a charge generating layer and a charge transporting layer accumulated thereon, the method comprising:
forming the charge generating layer using a coating liquid comprising oxotitanyl phthalocyanine as a charge generating material and having a turbidity in a range of from 180 to 350.
According to the intention, a photoreceptor which exhibits high sensitivity to the laser light and is capable of forming an image without generating an interference fringe due to laser light can be produced without deterioration in electric characteristics of the photoreceptor and increase in production cost.
In the invention it is preferable that the oxotitanyl phthalocyanine has major diffraction peaks at Bragg angles (2xcex8xc2x10.2xc2x0) of 7.3xc2x0, 9.4xc2x0, 9.6xc2x0, 11.6xc2x0, 13.3xc2x0, 17.9xc2x0, 24.1xc2x0 and 27.2xc2x0 in an X-diffraction spectrum.
According to the invention, a photoreceptor which exhibits high sensitivity to the laser light and is capable,of forming an image without generating an interference fringe due to laser light can be produced without deterioration in coating property, deterioration in electric characteristics of the photoreceptor, and increase in production cost.
In the invention it is preferable that in the X-ray diffraction spectrum of the oxotitanyl phthalocyanine, a bundle of peaks formed by the diffraction peaks at the Bragg angles (2xcex8xc2x10.2xc2x0) of 9.4xc2x0 and 9.6xc2x0 which overlap each other, is a maximum intensity of diffraction, and the peak at the Bragg angle (2xcex8xc2x10.2xc2x0) of 27.2xc2x0 is a second maximum intensity of diffraction.
According to the invention, a photoreceptor which exhibits high sensitivity to the laser light and is capable of forming an image without generating an interference fringe due to laser light can be produced without deterioration in electric characteristics and with improved coating properties, but not causing increase in production cost.
The formation of a film on an electroconductive support in a drum form is generally conducted by using a dip coating method. In the dip coating method, the support is immersed in a coating bath filled with the coating liquid for forming the charge generating layer, and then withdrawn therefrom. At this time, the Y value is controlled by the withdrawing rate. In the conventional coating liquid for forming a charge generating layer containing crystalline TiOPc, the change of the Y value with respect to the withdrawing rate is small, and thus it is difficult to control the Y value by the withdrawing rate. However, in the coating liquid for a charge generating layer containing crystalline TiOPc according to the invention, the change of the Y value with respect to the withdrawing rate is larger than that of the conventional one, and thus the Y value can be easily controlled. Therefore, the Y value within the range of the invention can be obtained by controlling only the withdrawing rate.